Strain the canned tuna with a fine sieve and a fork to force out the liquids. Discard the liquids.
In a medium bowl, combine strained tuna, green onions, Japanese mayo and sriracha sauce with a fork to make your spicy tuna filling. Taste test the filling and add more sriracha if you prefer it more spicy. Set aside.
In a large bowl with hot cooked rice, season with sesame oil, sesame seeds, and salt. Mix well. Cover with a damp towel or lid and keep warm at room temperature.
Vertically place a sheet of gim or nori rough side up and shiny side down on a cutting board (or on a bamboo sushi mat if you have one). Place 1 cup or a half portion the seasoned rice into the center of the gim or nori. Using clean hands or a rice paddle, evenly spread the portion of rice out and create a 1-inch border at the end furthest away from you.
Place two perilla leaves in the center of the rice, overlapping them so they can fit within the sheet of seaweed.
Scoop half of the spicy tuna mixture on top of the perilla leaves and evenly shape the tuna mixture into a thick log (see blog post for visuals). Do not spread it out thinly or when you roll it, the tuna filling will spill out from the sides. The tuna filling will eventually spread out evenly with enough rolling pressure.
Fold the perilla leaves over the tuna mixture, to hold the tuna mixture in.
Begin rolling the kimbap by starting at the end closest to you. Firmly roll and tuck the ingredients and be careful not to squeeze the tuna filling out as you roll. Once you reach the end, let the roll sit on top where the border was so it can stick to the rest of the roll with the residual heat from the rice.
Then evenly pour ½ teaspoon sesame oil on the kimbap roll and with clean hands or a brush, spread it all over the seaweed. Repeat the above steps for the remaining roll.
Next carefully brush or rub some sesame oil onto the sides of a sharp knife. Firmly hold the kimbap roll with your dominant hand (but don't squeeze) and slice it with the knife into 1-inch-thick pieces. Then garnish with sesame seeds. Enjoy!